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GCC provides an "undefined reference" link to static data elements in template classes that rely on default constructors

I have the same problem like this:

"undefined reference" for static specification of a field template

but the workaround that they use will not work for me.

I have a CRTP class with static data elements, one of which is std :: mutex. Unfortunately, the GCC linker (4.8.2) gives me the "undefined reference" error for this mutex. Klang (3.4) does not. Is there a workaround? The initial question (linked above) called the copy constructor on the static data member, which caused GCC to issue a character, but since my data member is std :: mutex, this is not an option - the copy constructor is deleted, and there are no argument constructors there. Have I just been with you?

I don't believe the problem is with std :: mutex, I think the problem is with how GCC handles static data members in template classes that rely on default constructors.

Thanks for any help!

Here's a thin version of my problem: test.hh

#include <mutex>

template < class T >
class CRTP_class {
public:
  T * ptr_;
  static std::mutex mutex_; // linker error here
  static int clearly_a_problem_with_mutex_; // no linker error here
};

class Foo : public CRTP_class< Foo >
{
public:
  void set_bar( int setting );
  int bar_;
};

test.cc

#include <test.hh>

template<> std::mutex CRTP_class< Foo >::mutex_;
template<> int CRTP_class< Foo >::clearly_a_problem_with_mutex_( 0 );

void Foo::set_bar( int setting ) {
  std::lock_guard< std::mutex > locker( mutex_ );
  ++clearly_a_problem_with_mutex_;
  bar_ = setting;
}

main.cc

#include <test.hh>

int main() {
  Foo foo;
  foo.set_bar( 5 );
}

:

g++ -std=c++0x main.cc test.cc -I.


/tmp/cclyxUfC.o: In function `Foo::set_bar(int)':
test.cc:(.text+0x86): undefined reference to `CRTP_class<Foo>::mutex_'
collect2: error: ld returned 1 exit status

(Edit 1: , , " " - , .cc .hh - , , , . , , # , , )

(Edit 2: Ooops! .)

+4
1

GCC bugzilla:

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=63876

, intializer . ,

template<> std::mutex CRTP_class< Foo >::mutex_;


template<> std::mutex CRTP_class< Foo >::mutex_{};

( .cc)

+4

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